The first such toad was captured on the island in December and since then, seven more have been captured or seen on the island, ministry officials said.

The toads, a very fertile breed about 15 cm long, are native to South America. They were introduced to neighboring Ishigaki Island in the late 1970s in an attempt to exterminate gold beetles, a sugar cane pest, and rapidly proliferated there.

The officials speculated the toads may have come to Iriomote from Ishigaki on a ship. Iriomote is some 460 km southwest of Okinawa Island.

Humans can be blinded by the poisonous fluid secreted by the toads, and mammals can die if they eat the toads, according to experts.

In an attempt to protect the 100 Iriomote cats estimated to live on the island, the ministry’s wildlife protection center is striving to exterminate the poisonous toads with cooperation from local residents.

Iriomote Island is the world’s only known habitat for the rare cats, which were confirmed as a new species of cat in 1967 and have since been designated as a protected species.

The ministry’s center is distributing leaflets to the island’s inhabitants to seek information on toad sightings.

Masaya Tatara, an official at the center, said the center will conduct field research before summer, the breeding period for the toads.

Now recognized as a growing problem in Japan, the Environment Ministry plans to create a panel of experts to set guidelines on the handling of imported species that threaten native animals or local ecosystems.

The problem has been compounded in recent years by Japanese pet lovers who buy exotic species from pet shops only to let them go when the animals grow bigger or get out of control.

One of the common features of these imported species is their enormous fertility.

For example, the number of Java mongoose brought to Amami Oshima Island to combat the poisonous “habu” snakes has increased to roughly 10,000, prompting the ministry to start work five years ago to eradicate the animal from the island.